Openwork seat back



FIG. 1 is a rear elevational view of an openwork seat back showing my new design, the front view being a mirror image;

FIG. 2 is a right side elevational view thereof, the left side being a mirror image thereof;

FIG. 3 is a top plan view thereof; and,

FIG. 4 is a bottom plan view thereof. 

The ornamental design for an openwork seat back, as shown and described. 